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Operation
F-FEM-CON — User’s Guide
The evaluation method in the firmware always uses a sampling rate of 1 kHz.
However, as values between 1 Hz and 1 kHz can be set as update rates, the
software calculates an average if the update rate is lower than the input
frequency. The errors or inaccuracies are not influenced by this and are as
described above!
With this software system, theoretically, the maximum input frequency (= speed
* number of teeth) may increase up to half the reference frequency (i.e. 10 MHz).
However, it is practically impossible to reach this value because it is limited to
approx. 1 MHz (according to encoder type) by the input circuit.
The minimum input frequency is only determined by the accuracy of the calcula-
tion of the processor and can thus also result in values that tend to come close to
zero.
With speeds that low, counting pulses are not generated during every measuring
interval. Thus, it is necessary to increment the accumulated time (i.e. the
measuring intervals) that has passed since the latest occurrence of a counting
pulse to be able to calculate a fictitious speed. When the next counting pulse is
generated, the actual speed is calculated again. This calculation method is used
to simulate the coasting of an engine.
As soon as one counting pulse is generated per measurement interval, this
incrementation of measuring intervals no longer takes place because a new
value can be calculated.
Standstill recognition must thus be performed by the automation system. The
threshold for the zero speed can be adjusted to meet the requirements.
Compared to the AB channels, the zero track for the incremental encoder input
is an exception because it recognizes only the occurrence of exactly one pulse
per measuring interval (1 ms). The resulting maximum frequency is 500 Hz. This
value is sufficient because this pulse is generated only once per revolution. This
corresponds to a maximum speed of 30000 rpm.
Example
Using an incremental speed encoder with 1024 marks, an input frequency of
1 Hz corresponds to a speed of 0.029 rpm.
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